The approaches described in this section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Event correlation technology is commonly used by network management systems (NMS) to enhance various diagnostic and other analytic operations. A purpose of correlating events in a network is to determine whether events are related to each other. By grouping related events, the management of a network becomes less daunting. For example, 100 events occur in a network in a ten-minute span. If a network administrator could determine that the 100 events could be partitioned into only three groups of related events, then the task of analyzing three groups of events is a significant reduction in work compared to analyzing 100 events in isolation.
A NMS may employ several techniques to correlate network events, such as a physical link between two routers going down. Event correlation techniques include geographical area correlation, which attempts to correlate events based on geographical proximity of events, time-based correlation, which relies on time stamp of events to achieve correlation, and rule-based correlation, which allows case by case correlation.
Another such technique is topology-based correlation, which is considered to be a highly accurate and reliable approach in correlating network events. According to one topology-based approach, event correlation is performed using a computer system or application that interacts with a “virtual network,” which is an in-memory model of an actual network. The virtual network includes virtual network elements (VNEs) that represent corresponding network elements (such as switches and routers) in the actual network. The virtual network also models network topology and regular functions of the actual network, such as network services.
In order to perform event correlation, an NMS simulates network traffic flows within the virtual network. Topology-based event correlation is performed by simulating these network traffic flows (referred to herein as “flows”) through the topological links among VNEs.
For diagnostic purposes, such as root cause analysis (RCA), the topology of interest is usually at the physical level, where actual physical network links are traversed. For that purpose, the virtual network models the actual physical topology over which a NMS simulates flows. A NMS may also maintain and use logical topology links to enable traversal of large network segments in a single hop.
A network service provider (or simply “provider”) may provide services to its customers that require connectivity over the provider's network as well as over network segments that are not owned and/or are not managed by the provider. Segments of a network that are owned and/or managed by a provider are referred to herein as “managed segments” with respect to that provider. Network segments that are not owned and/or not managed by a provider are referred to herein as “unmanaged segments” with respect to that provider.
For many analytic and monitoring purposes, the unmanaged segment can still be modeled with a single VNE (referred to herein as a “cloud VNE”). However, a cloud VNE is only visible as a layer 3 (IP) element in the seven-layer Open Systems Interconnect (OSI) model of network elements. A cloud VNE may represent elements that are layers 1, 2, and 3. A cloud VNE is technology-dependent on whether the cloud VNE can be implemented: if enough information exists at the edges of an unmanaged segment, then creating a cloud VNE for that unmanaged segment is possible; otherwise, creating a cloud VNE for that unmanaged segment is impossible.
The physical and logical structure of an unmanaged segment is unknown to the NMS. The use of a cloud VNE is also limited because a service provider using a NMS typically chooses not to deploy a cloud VNE for various reasons. When a cloud VNE is not deployed, simulating a flow by traversing a path through both managed segments and one or more unmanaged segments is not possible, without the full mapping of the physical topology across the complete network. Even in some cases where a cloud VNE is present, traversal of the cloud VNE may not be possible.